The present invention relates to an amplifier for amplifying various signals, which amplifier is capable of switching on and off its output signal.
It is known to connect a switching circuit to the output of an amplifier circuit to provide the amplifier circuit with the additional function of switching on and off the output signal of the amplifier circuit. Such an amplifier is constructed by connecting a conventional switching circuit, such as a switching circuit employing a diode bridge, as disclosed in Japanese Patent Laid-open (Kokai) No. 54-148358, to a conventional amplifier circuit. In operation, the amplifier provides its output signal when a current is supplied to the diode bridge, and inhibits the output signal when the current supplied to the diode bridge is reduced.
A current which is 1 to 1.5 times greater than the maximum current of the amplifier must be supplied continuously, regardless of the intensity of the output current, to the diode bridge of the switching circuit to accommodate the function for switching on and off the output signal to the amplifier circuit. Amplifiers having an amplifier circuit and a diode bridge in combination therefore operates at a low current efficiency and requires large power, which proves to be a significant disadvantage, particularly when the output current has a high peak value and a small mean value, and in the worst case makes it impossible to design a practical circuit.
Furthermore, the allowable current of the component diodes of the diode bridge must be 1 to 1.5 times greater than the maximum current of the amplifier. The diodes have large dimensions and a large parasitic capacity, and hence, it is difficult to construct a high-speed amplifier with such a switching arrangement.